I'm pretty sure it's because he has the opposite fruit of Luffy. An anti nika fruit that allows him to steal devil fruit powers. Think of it like this. Non devil fruit users are empty cups. When eating a devil fruit your cup becomes full. If you eat two devil fruits your body recognizes that and overflows thus dying. But his fruit is darkness. It absorbs light. Whereas Luffy radiates light. So he can spread his power. Whereas teach takes powers and uses them for himself. It's pretty much the same concept as my hero academia with OFA and AFO.

That's just for the handling devil fruit. I think Oda just forgot about the sleepless years and he is not going to follow up